1. Field of the Invention
The present invention relates to a process of improving the whitening, and thus color, of tampon applicators. In particular, the present invention relates to a process that whitens or maintains the whiteness (color) of polymeric tampon applicators, especially biodegradable tampon applicators.
Tampon applicators are conventionally manufactured either of a plastic, a cardboard or a paper based material. Plastic tampon applicators are typically manufactured by using an injection molding process. The injection molding process allows desirable features, such as a petal shaped expulsion end and a finger grip to be molded into any desired shape to provide a reliable and high quality product.
A disadvantage of some known plastic tampon applicators is that the plastic material is not biodegradable. While such applicators flush, they do not decompose. Therefore, such applicators may accumulate in septic tanks or on screens in wastewater treatment plants and may cause blockages. In addition, plastic tampon applicators typically neither float nor settle to the bottom of settling tanks so they are not easily removed as sludge or by skimmers.
2. Description of the Prior Art
One plastic material that is dispersible in water and that has been used for tampon applicators is polyvinyl alcohol. Polyvinyl alcohol plastic material for use in tampon applicators is described, for example, in U.S. Pat. Nos. 3,882,196, 3,911,917 and 5,002,526. However, polyvinyl alcohol suffers from discoloration, as well as a strong vinegary odor as described in U.S. Pat. No. 3,882,196 at column 1, line 25 et seq. As further described in U.S. Pat. No. 3,882,196, these problems are resolved prior to injection molding by adding to the polyvinyl alcohol a proton acceptor, such as titanium dioxide, to eliminate the odor, and a white pigment to improve the color to an off-white color. The off-white color, though an improvement, is not pleasingly aesthetic to many women.
U.S. Pat. No. 3,657,533 provides a process of preparing bilaterally oriented films of polymers of ethylene (heat shrink films). The process includes a step of irradiating plastic tubing by means of an electron beam for cross linking to provide strength uniformly in the finished heat shrink film product.
U.S. Pat. Nos. 5,473,165 and 5,532,495 provide ion beam generators that produce an ion beam characterized by pulses of ion energy for a variety of applications including the modification of the near surface microstructure of various materials including polymers.
U.S. Pat. No. 5,454,801 provides a process for forming a polymer coating for the cover of absorbent articles such as sanitary napkins, diapers and the like. The coating is formed of a polymer into a liquid phase and then foamed, either before or after coating, onto the substrate. The foam can be prepared by cross-linking polyethylene and polypropylene either chemically or by radiation provided by an electron gun and then curing the cross-linked polymer by heating. Whiteness of the coating is improved by adding white pigment prior to curing. The curing operation may be performed by means of radiant or thermal energy, for example, heat, ultraviolet light or electron beam.
U.S. Pat. No. 5,171,762 provides a process that improves the APHA color (yellowness) of a polymer, particularly polytetrahydrofuran, by subjecting the polymer to microwave energy for a sufficient time to melt the polymer.
Thus, the prior art has improved the whiteness of a polyvinyl alcohol tampon applicator by adding white pigment to the polyvinyl alcohol prior to injection molding with the result of an off-white color that is not pleasingly aesthetic to many women. Also, the prior art has irradiated the surface of polymers for the purpose of cross-linking with pulsed ion beams, has prepared foamed polymers by cross-linking with radiation provided by an electron gun, has cured foamed polymers with radiant or thermal energy, for example heat, ultraviolet light or electron beams. Such methods have affected the polymer and are also believed to be expensive. The prior art has attempted to improve the yellowness of polytetrahydrofuran by applying microwave energy for a sufficient time to melt it. Therefore, none of the prior art has improved the whiteness of plastic tampon applicators by simple surface treatment after injection molding.
It is an object of the present invention to provide a process that improves the whiteness or color of a polymeric tampon applicator.
It is another object of the present invention to provide such a process that provides a surface treatment to the tampon applicator after injection molding to improve its whiteness.
It is still another object of the present invention to provide such a process that subjects the surface of the tampon applicator to electron beam radiation to improve whiteness.
It is a further object of the present invention to provide such a process that i s relatively inexpensive.
These and other objects of the present invention will be accomplished by the process of the present invention that improves the whiteness of a polymeric tampon applicator by applying to its surface a beam of electrons, sufficient in energy and time duration to whiten the color of the tampon applicator. The tampon applicator is preferably a biodegradable tampon applicator. The preferred biodegradable tampon applicator is made of polyvinyl alcohol.